Prior art methods of making hollow, resinimpregnated fibrous articles are expensive, time consuming, laborious to use and have poor dimensional accuracy. In addition, the tools could be easily damaged requiring constant repair. For example, in methods using plaster of paris mandrels, the mandrel is first poured in a separate mold. The resin impregnated fibrous material is then layed up on the plaster mandrel and the material is covered with a tape that shrinks as the temperature is increased. During the oven cure the force exerted on the material varies depending upon how uniformly the tape was applied. Also, variations in the cure temperature and compressive load induced by the shrinking tape cause variations in the surface finish of the cured article. After curing, the plaster mandrel is removed from the article by breaking it into small pieces, using a hammer, chisel, or by drilling. This is a tedious, time consuming and costly operation without assurance that the article itself will not be damaged. Furthermore, if the article being formed is long and thin, the plaster mandrel becomes so delicate that extreme care is necessary to handle it. A new mandrel must be formed and destroyed for each part.
Another method uses an inflatable-collapsible mandrel which is first inflated to the internal dimensions of the article to be manufactured, over which the resinimpregnated fibrous material is layed up. Using this type of mandrel, the layup cannot be applied by a filament winding operation because the high compression loads caused by the filament or tape tend to deform the mandrel. Furthermore, since the mandrel is inflated with a gaseous medium, the mandrel does not maintain an exact shape during curing of the article. This results in a loss of dimensional accuracy. Often, because of the drawbacks of these prior methods, local external or internal reinforcements are layed up and cured in separate steps. This greatly increases the cost of the part. Some configurations are completely impractical to manufacture by prior methods.